Field of the Invention
In general the invention relates to extending the depth of field in images. More particularly, the invention relates to an imaging apparatus, having an automated extended depth of field mode, and associated method.
Background Information
Obtaining sufficient depth of field is a constant challenge in photography, particularly when photographing at extremely close range or under low lighting conditions. Setting the lens to a small aperture yields more depth of field, but this technique is eventually limited by diffraction effects and may mandate excessively long exposure times. The traditional approach to this difficulty required the photographer to “determine the optimum lens aperture for effecting the golden mean between stopping down the lens for depth of field and opening it up for good resolution”. Close-up Photography & Photomacrography 78 (Kodak Technical Publication N-12, Eastman Kodak Co. 1977).
However, advances in image post-processing have enabled a new approach to this challenge. In extended depth of field (EDOF) photography, a photographer captures a “stack” of images, sweeping the focus distance of the lens through the range of interest in a stepwise fashion. Post-processing software then combines the stack images into a single composite image by selecting from each stack image the in-focus portion of the image. The resulting composite image thus provides both high resolution and a large depth of field. However, this technique requires the photographer to determine the depth of field provided by the lens and aperture, and to then manually advance the focus distance of the lens by the appropriate amount between acquisition of each stack image. This is both tedious and prone to error.
Software control programs are available that control camera systems to produce image stacks, wherein each image is taken at different focus points within the subject. However, the software programs run externally to the imaging apparatus, therefore requiring a separate computing apparatus, communicatively coupled to the imaging apparatus for executing the control software. Additionally, the task of mastering such control programs may be difficult and time-consuming. Furthermore, such programs are not widely available, typically being provided by manufacturers or VAR's (value-added resellers) for specific imaging apparatus.
Digital cameras having an automated focus bracketing feature are now available. In photography, “bracketing” is the general technique of taking several shots of the same subject using different camera settings. A camera having an automated focus bracketing capability takes a series of shots of a subject, automatically changing the focal distance after each shot. Typically, the photographer may choose from a number of settings that specify the number of shots. Such bracketing features do not embody automated intelligence for calculating the spacing of images in a stack for (EDOF) photography based on photographer-selected near and far focus limits.